Generator sets (gensets) are self-contained power modules that can be permanently or temporarily connected to an offboard facility, for example to a home, a hospital, or a factory, to provide primary, supplemental, and emergency backup power to one or more external loads. Cables extend from a distribution grid of the facility to the gensets and are selectively connected to the gensets by way of load interruption devices. A genset controller, typically mounted on each genset, monitors and responsively controls characteristics of electric power produced by each genset and sent to the offboard facility.
In some situations, the voltage and/or current produced by a genset may be too high for the genset controller to directly measure. In these situations, one or more current and/or voltage transformers may be used to step down the voltage and current to lower levels, which may be more readily accepted by the controller. In order for each genset to provide power having characteristics desired by a customer, each genset controller should accurately measure the stepped down and converted power and properly correlate this power to the power produced by the associated genset. Unfortunately, the different sensing components and circuitry within the controller, as well as the different transformers that provide the stepped-down power to the controller, can introduce shift, scale, and delay errors into the measurements made by the controller. Accordingly, the controller may require calibration for optimum performance.
Historically, calibration of a genset controller has been performed manually. That is, power from a genset was directed through a metering device simultaneous with readouts from a corresponding genset controller. If scale or time delay errors between the measured genset power and the controller readouts were observed on the metering device, a technician could then adjust settings of the genset controller such that the errors were reduced. Although satisfactory for some applications, this manual calibration process was time consuming and had an accuracy level too low for other applications.
A method of calibrating a power meter device is disclosed in U.S. Pat. No. 7,660,682 (the '682 patent) of Slota et al. published on Feb. 9, 2010.Specifically, the '682 patent discloses a metering device having transformers for stepping down and converting from AC to DC electrical energy in a power line, circuitry for measuring a parameter of the transformed electrical energy, a storage device for storing a calibration factor, and a processor for processing the calibration factor and adjusting the measuring of the parameter to compensate for scale and time delay errors caused by the transformers and the circuitry. In a first mode of operation, which occurs at a factory, errors generated by the circuitry are determined and calibration factors are calculated that will be used during a second mode of operation to compensate for the circuitry-generated errors. During a third mode of operation, which occurs after the circuitry is connected to the transformers at a substation, the processor applies different known voltages and/or currents to the transformers at a number of different test points and measures outputs of the circuitry. The measured outputs are compared to expected outputs and corresponding error values are determined. The processor then determines adjustments for compensating for the errors at the test points. The storage device stores the calibration factors and the adjustments, and the circuitry references and implements the stored information during parameter measuring in the second mode of operation.
Although the method of the '682 patent may be helpful when calibrating a power meter, the benefit thereof may be minimal. In particular, the method may still rely on a manual calibration process completed at a factory, which, as described above, can be time consuming and have low accuracy. In addition, the test points utilized by the processor at the substation may not be selected to provide a sufficiently accurate determination of error. Further, the method of the '682 patent makes a comparison with expected values during the third mode of operation, which can be problematic if the expected values do not properly match actual values. Finally, the method of the '682 patent may not be applicable to a genset controller.
The disclosed calibration controller is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.